Sag vertical curve: low point, overhead clearance and the drainage check
A 500 ft sag curve is reduced to a grade sheet, the low point is located for drainage, clearance under an overhead structure is verified, and the flat zone around the low point is measured against a 100 ft criterion.
Analyze· about 28 minutes by hand· 5 steps
Given
An equal-tangent parabolic sag curve carrying a curbed roadway.
Grade in g₁ = −3.50 percent; grade out g₂ = +1.80 percent.
Curve length L = 500.00 ft.
PVI at station 61+00.00, elevation 428.60 ft.
An existing structure crosses the roadway at station 60+50.00. The underside of its beams is at elevation 447.10 ft, and the required vertical clearance is 14.50 ft.
Drainage policy: the profile grade must be steeper than 0.30 percent except over a length of at most 100 ft either side of the low point taken together.
Elevations to 0.01 ft.
Required
Stations and elevations of the BVC and the EVC, and the curve constants.
Station and elevation of the low point.
A grade sheet at full stations.
Whether the clearance under the structure is met.
The length of profile over which the grade is flatter than 0.30 percent, and whether it passes the drainage criterion.
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